1. Field of the Invention
This invention relates to ingot mold cars, commonly referred to as buggies in the steel industry, for transporting ingot molds and/or the ingots formed therein.
After the molten metal has been poured into molds and has solidified as ingots in the molds, the drag of molds with the ingots therein is moved to the strippers. The strippers are usually overhead cranes. In the case of molds of the big end down design, which have open bottom ends, the cranes lift the molds individually from the ingot buggy while a plunger forces the ingot downwardly against the platform of the buggy. In the case of molds of the big-end-up design, which have open tops, the cranes lift the ingot from the mold while holding the mold down against the buggy. After the big-end-down molds or big-end-up ingots are lifted away they are transferred to other buggies. Frequently, there occur "stickers", i.e., ingots which cannot be readily released from the molds. Such stickers usually occur in molds whose inside surfaces have eroded unevenly and wherein some of the molten metal fills in the eroded areas and form sprues extending into the sidewalls of the molds. In such events, it is a very common practice to lift the mold and the ingot several feet above the buggy and drop them upon the deck of the buggy. Although this loosens the ingots from the mold, such practice is very damaging to the buggy and shortens its useful life. The dropping of the combined ingot and mold produces a large amount of foot pounds of energy, which energy must be absorbed by deflection of the various components of the buggy in order to stop the free fall of the combination.
2. Prior Art
In a typical prior art ingot mold buggy there is a single deck frame supported by substructure which includes a pair of center thrust bearings and bolster assemblies for cushioning dynamic load effects upon the wheel axle journals. In such buggy the weight of the carried load, the weight of the deck frame, and the weight of the substructure, as well as any impact loading, are all imposed on the center thrust bearings. In turn the load on each of these bearings is borne by a truck frame which carries wheels of the buggy and the bolster assemblies. Each of the bolster assemblies comprises a series of helical compression type springs which transmits the load downwardly to the wheel journal bearings.
Generally, any sizable loading will cause the helical springs to deflect. If a sufficiently great loading, such as a dynamic one caused by dropping an ingot mold and a contained ingot, is imposed the springs will be momentarily completely compressed to the point where they form solid cylinders. Any loading greater than that required to completely close the coils of the springs will result in increased deflection of other components of the buggy. Since the other components are usually of rigid construction there need not occur great physical deflection before such components will be strained beyond the elastic limit of the material of which they are comprised and take on a permanent set and irreversible deformation. Such deformation ultimately destroys the useful life of the buggy.